Until the mid-1980s, the accepted treatment for atherosclerosis, i.e., narrowing of the coronary artery(ies) was coronary by-pass surgery. While effective and evolved to a relatively high degree of safety for such an invasive procedure, by-pass surgery still involves potentially serious complications and in the best of cases an extended recovery period.
With the advent of percutaneous tranluminal coronary angioplasty (PTCA) in 1977, the scene changed dramatically. Using catheter techniques originally developed for heart exploration, inflatable balloons were employed to re-open occluded regions in arteries. The procedure was relatively non-invasive, took a very short time compared to by-pass surgery and the recovery time was minimal. However, PTCA brought with it other problems such as vasospasm and elastic recoil of the stretched arterial wall which could undo much of what was accomplished and, in addition, it created a new disease, restenosis, the re-clogging of the treated artery due to neointimal hyperplasia.
The next improvement, advanced in the mid-1980s was the use of a stent to maintain the luminal diameter after PTCA. This for all intents and purposes put an end to vasospasm and elastic recoil but did not entirely resolve the issue of restenosis. That is, prior to the introduction of stents, restenosis occurred in from 30-50% of patients undergoing PTCA. Stenting reduced this to about 15-20%, much improved but still more than desirable.
In 2003, drug-eluting stents or DESs were introduced. The drugs initially employed with the DES were cytostatic compounds, that is, compounds that curtailed the proliferation of cells that resulted in restenosis. The occurrence of restenosis was thereby reduced to about 5-7%, a relatively acceptable figure. However, the use of DESs engendered a new problem, late stent thrombosis, the forming of blood clots long after the stent was in place. It was hypothesized that the formation of blood clots was most likely due to delayed healing, a side-effect of the use of cytostatic drugs.
What is needed is an implantable medical device that includes a pro-healing influence to counter the delayed healing due to the eluting drugs. While this would be particularly useful with regard to coronary stents, it would also provide substantial benefit to any manner of implantable medical device. For instance, it has been stated that the occurrence of restenosis in the case of lower extremity percutaneous angioplasty is particularly unacceptable (Paul S. Teirstein, Circulation, 2000, 102:2674) and it would be expected that this situation would also be amenable to the effects of stents having pro-healing properties. The present invention provides such implantable medical devices.